The spine consists of a series of bone structures termed “vertebrae.” Between each vertebra is a flexible, connective tissue termed an “intervertebral disc” which secures one vertebra to another and functions as a shock absorber. Spinal fixation is a surgical technique in which one or more of the vertebrae of the spine are joined by an implant (e.g., a plate or rods.) to prevent relative movement of the spine, with the goal of live bone eventually fusing the adjacent vertebrae together.
Patients requiring spinal fusion typically suffer from either neurological deficits or severe pain which has not responded to conservative treatment. Typical conditions that are treated by spinal fusion procedure non-exclusively include: degenerative spinal conditions, discogenic pain, spinal tumor, vertebral fracture, scoliosis, kyphosis, spondylolisthesis, spondylosis, and other conditions that causes instability or pain in the spine.
Typically a spinal fixation procedure does not connect the patient's original vertebrae directly together; rather the intervertebral disc is usually completely or partially removed (disectomy) and/or one or more entire vertebral bodies are removed (corpectomy). The space remaining from the removed discs and vertebral bodies after a disectomy or corpectomy is typically replaced by a graft positioned between adjacent vertebrae to maintain proper length in the spinal column. After the surgery, it is desired that living bone from the vertebrae spans the inter-body graft thereby fusing the adjacent vertebrae together.
Traditionally, interbody grafts are fashioned from bone taken from a patient's skeleton, and are also referred to as “autografts.” As the harvesting of an autograft is painful for the patient, many surgeons now prefer the use of “allografts” which are harvested from a body other than the patient's. Interbody grafts may also be formed from synthetic materials such as titanium, carbon fiber and plastics. Unfortunately, grafts are associated with a relatively high rate of dislodgement due to the patient's neck movement during the healing process. To minimize the risk of dislodgement of the interbody graft posteriorly, toward the spinal cord, surgeons routinely mortise the graft by drilling a shelf into the vertebrae. To minimize the risk of dislodgement of the interbody graft anteriorly, surgeons routinely place a fusion plate across the inner space and secure it with screws extending into the vertebrae.
Placement of an anterior cervical plate with a screw fixation is effective in preventing interbody graft dislodgement toward the esophagus and also enhances fusion by providing rigid fixation between the vertebrae.
Presently, in performing a disectomy or corpectomy, a distractor is used to spread the adjacent vertebrae so that the disc or vertebral body of interest can be removed. In use, a pair of distractor pins having heads for engaging with a distractor are screwed into the vertebrae adjacent to the disectomy or corpectomy site. One pin is placed in the superior vertebra, and a second pin is placed in the inferior vertebra. The distractor is then coupled to the heads of pins on the upper and lower vertebrae, above and below the site, and the vertebrae are then mechanically spread apart, for aiding in the removal of any remaining portion of the deteriorated disc or vertebral body, and also for creating a gap for placing the graft. According to most traditional methods, the distractor and distractor pins are removed after the bone graft is positioned, and before a fusion plate is fixed onto the lower and upper vertebrae.
The above-described method has many disadvantages, one being that it relies on the natural weight of the spine to compress the intervertebral graft between the upper and lower vertebral bodies. Natural compression alone is often insufficient as it can create undesirable space between the vertebral members and thus reduces the likelihood that fusion will occur. U.S. Pat. No. 6,648,891, to Kim (which is hereby expressly incorporated by reference herein in its entirety) attempted to address this issue by describing a system that allows a slotted fusion plate to be screwed into the desired vertebral bodies while the distractor and the distractor pins remain in the vertebrae (See Kim, cols. 2-3). More specifically, these plates include the upper and lower slots configured to be used with distractor pins, and therefore allow a surgeon to utilize a distractor to apply “mechanical compression” on the intervertebral graft as the final fusion plate is secured.
Unfortunately, the fusion plates provided by Kim are not a complete solution. Even though the slotted plates are configured to be used while the distractor pins are still attached to the vertebral bodies, they do not allow for an unobstructed view of the spine, including the intervertebral space where the graft is positioned during the operation. Without an unobstructed view, surgeons are more likely to accidentally position the screw into the graft, which could push it into the patient's spinal cord. It is important to note that adding a central window to the Kim plates would not be an obvious modification. To explain, it is first noted that the screw holes on the plate need to be of a considerable size to accommodate the final screws. This is important because the width of the plate is limited by the width of the vertebral bodies, and thus there is a limited amount of space on the plate for both upper and lower slots and the screw holes. Due to this constraint, the bigger the screw holes are on the plate, the less available space there will be for the slots, and vice versa. This sizing and positioning problem is compounded if the final plate also includes a central window for viewing the graft. Having a large viewing window, screw holes, and distractor pin slots on the final plate can also compromise the strength of the final plate, especially if it is a smaller sized plate.
Thus, there is a need in the art for improved procedures and systems for applying a fusion plate to a patient's spine, following a corpectomy or disectomy, that provide sufficient pressure to the spine and an optimum viewing area for the surgeon to work, without utilizing potentially weakened, or poorly configured plates.